nil check for owner and trackable

lib/public_activity/activity.rb

@@ -42,12 +42,19 @@ class Activity < ActiveRecord::Base
     def text(params = {})
 
       #make all the fields of the owner and trackable object automatically avaialable
-      self.trackable.attributes.each do |key, value|
-        params[key.to_sym] = value
+
+      if !self.trackable.attributes.nil?
+        self.trackable.attributes.each do |key, value|
+          params[key.to_sym] = value
+        end
       end
-      self.owner.attributes.each do |key, value|
-        params[key.to_sym] = value
+
+      if !self.owner.attributes.nil?
+        self.owner.attributes.each do |key, value|
+          params[key.to_sym] = value
+        end
       end
+
       parameters.merge! params
 
       I18n.t(key, parameters || {})